Air actuator



April 19, 1966 P. CARR 3,246,581

AIR ACTUATOR Filed Oct. 25, 1963 2 Sheets-Sheet l 2' 25 lo I 5, \2

26 Fig. 2+=-- Fig 2 I INVENTOR.

BY Poul Carr wfwm/ ATTOR/V E Y5 P. CARR AIR ACTUATOR April 19, 1966 2. Sheets-Sheet 2 Filed Oct. 23, 1963 INVENTOR BY Paul Corr ATTORNEYS United States Patent 0 3,246,581 AIR ACTUATOR Paul Carr, Uniontown, Ohio, assignor to Flo-Turk, lnc., ()rrville, Ohio, a corporation of Ohio Filed Oct. 23, 1963, Ser. No. 318,266 16 Claims. (Cl. 92136) This invention relates generally to fluid actuators, and more specifically to new and useful improvements in rotary fluid actuators.

The present invention is particularly concerned with improvements in rotary actuators of the type comprising a cylinder, a pinion between the ends of the cylinder, and a piston and rack mechanism reciprocally disposed in the cylinder within meshing engagement with the pinion. In actuators of this type, the pinion is customarily fixed on a suitably journaled output shaft so that alter nate introduction of fluid under pressure into opposite ends of the cylinder causes reciprocation of the piston and rack assembly, thereby rotating the pinion and output shaft in a selected direction.

In the manufacture of actuators, there is a need for great versatility in the size and capacity of actuators manufactured. These actuators are employed in a wide variety of applications and for this reason there is great variance in requirements as to the torque required in a given application and as to the amount of rotation required.

In US. patent application Serial No. 258,824, filed February 1S, 1963, by Kenneth H. Meyer and Paul Carr, under the title Actuator, now Patent 3,156,160, issued November 10, 1964, there is a disclosure of a versatile actuator design which is best suited for use as a hydraulic actuator. In that application, there is a teaching of an actuator construction in which one housing may be used for a variety of sizes of actuator. Tubing cut to appropriate length is used to provide cylinders of appropriate and selected length. The manufacturer under the teaching of that invention is able, then. to fabricate an actuator to a given customers needs from a relatively small number of stock items.

The present invention applies the same fundamental concept of a construction which permits fabrication of actuators to a customers specification. Thus, here, as in the referenced application, tubing may be cut to appropriate and predetermined lengths to provide cylinder. A novel construction here permits the rack to be formed of standard commercial rack stock and, like the tubing, cut to appropriate length and then secured to pistons in a manner which Will be described presently. While the present disclosure will be directed to a so-called single rack and piston unit, it will be appreciated that it is applicable to a construction wherein there are a pair of racks disposed on opposite sides of the pinion to provide balanced torque application to the pinion in the manner i described in more complete detail in the referenced application.

An object of the invention is to provide a new and improved actuator construction of the type generally described which is versatile, compact, relatively simple, and inexpensive.

Another object of the invention is to provide a new and improved actuator construction of the type generally described which is easy to repair and which can be readily modified to change the amount of rotation of the pinion.

A further object of the invention is to provide a new and improved actuator of the type described including a novel rack assembly which is positioned in the cylinder and connected to the pistons in such a manner that the separation forces between the rack and pinion are not transmitted to the pistons, thereby assuring that the pisice tons will not cock and bind in the cylinder because of high torque loading.

A more specific object of the invention is to provide an actuator as described in the previous paragraph wherein the rack assembly is connected to the pistons by lost motion connections so that the rack assembly is freely supported and limited floating movement of the pistons relative to the rack assembly is permitted.

Still another object of the invention is to provide an actuator having arack assembly as described in any of the previous paragraphs and which is further characterized by a novel bearing structure between the bottom of the rack and the inner wall surface of the cylinder so that the rack is prevented from bending during operation of the actuator and backlash between the rack and pinion is controlled.

The foregoing objects are attained by a new and improved construction including a rack formed from conventional rack stock and having a length selected to cause the desired amount of pinion rotation. The rack is offset from the axis of the cylinder and is attached to the pis-. tons by structure which forms lost motion connection. The lost motion connections are located on the cylinder axis and are formed so that the pistons are free to float a limited distance relative to the rack assembly. With this preferred construction, the pistons are self-centering and the forces tending to separate the rack and pinion during operation are not transmitted to the pistons so as to cause misalignment and cocking in the cylinder- The invention also contemplates a novel bearing support between the rack and the cylinder which supports the rack independently of the pistons and prevents it from bending during operation of the actuator. Preferably, the bearing support is formed by plastic rack sliders which are pinned to the bottom of the rack and disposed in sliding engagement with the inner wall surface of the cylinder. This preferred construction is such as to permit additional rack sliders to be added when the rack length is increased, thereby effectively preventing racks of any length from bending under unsupported loads. In addition to supporting the rack as a free member and preventing it from bending, the novel rack sliders effectively control backlash between the rack and pinion.

The foregoing features of the invention are embodied in a preferred actuator arrangement including a tube which is closed at its ends to form the cylinder in which the pistons and rack assembly are disposed. A central housing is provided between ends of the tube and the pinion, which is also positioned in the cylinder tube, is journalled in the housing. This actuator construction is compact, relatively simple, and inexpensive. At the same time, the construction has the advantage of providing versatility since cylinder tubes of different sizes can be substituted for use with the same housing and pinion assembly. For example, when it is desired to employ a long rack to increase the amount of pinion rotation, it is a simple matter to substitute a longer cylinder tube and to mount the piston and rack assembly in the tube.

Other objects and advantages of the invention will become apparent from the foregoing detailed description when taken in conjunction with the accompanying drawmgs.

In the drawings:

FIGURE 1 is a cross-sectional view showing an em bodiment of this invention and is taken on the line 11 of FIG. 2;

FIGURE 2 is a cross-sectional view taken on the line 22 of FIG. 1; and

FIGURE 3 is a horizontal, cross-sectional view of the embodiments shown in FIGS. 1 and 2.

Referring now to the drawings, there is shown a rotary fluid actuator ltl embodying the present invention. The

illustrated construction of the actuator includes a cylinder tube 11 which may be formed of brass or other suitable material. The ends of the tube 11 are closed by end caps 12 made of steel or the like which are provided with ports 13 through which fluid under pressure can be alternatively introduced into the ends of the cylinder to drive the pistons. The end caps 12 are formed with annular sealing portions 14 which carry O-rings 15 and into which the ends of the cylinder tube are telescoped. Tie rods 16 extend the length of the actuator 10 through holes in the end caps 12, and nuts 17 are threaded on the ends of the tie rods to clamp the end caps against the ends of the tube 11.

In the construction shown, a split housing is provided between the ends of the cylinder tube 11. The halves of the split housing 25 are assembled around the tube 11 and are secured together by bolts 26. The tube 11 is formed 'with side wall openings 28 and each half of the assembled housing 25 has an opening 29 which is defined by a radial flange 30 and is in alignment with the side wall openings 28.

A pinion is disposed within the tube 11 and is fixed on a sleeve 36 which extends through the openings 28, 29. As shown in FIG. 3, the sleeve 36 is adapted to be secured on an output shaft 37 which may extend from one or both sides of the actuator 10. The sleeve 36 is journalled in needle bearings 38 which are carried by annular bearing caps 39 mounted within each half of the housing 25 against the radial flanges 30. Thrust washers 40 are mounted between the bearing caps 39 and shoulders 41 formed on the end portions of the sleeve 36. Each bearing cap 39 also carries an O-ring 42 in sealing engagement with the sleeve.

As generally described above, a piston is reciprocally disposed in the tube 11 between each of its ends and the pinion 35. Each piston carries an annular sealing member 51. A rack 52 which is offset from the axis of the cylinder tube extends between the pistons 50 and is in meshing engagement with the pinion 35. Preferably, the rack 52 is cut from commercially available rack stock so that it can be inexpensively replaced.

In accordance with this invention, bearings or rack sliders 53 are secured to the bottom of the rack 52 by pins 54a and are in sliding engagement with the inner wall surface of the tube 11. The rack sliders 53 are preferably formed of suitable plastic bearing material such as Delrin (an acetal resin derived by polymerization of formaldehyde), nylon, or the like. The length of the sliders 53 is sufficient to support the rack 52 so that it 'will not bend during operation of the actuator and so that the lateral forces tending to separate the rack and pinion and will not be transmitted to the pistons. Additional sliders 53 can be added as desired when the length of the rack is increased.

The rack 52 is connected to the pistons 50 by structure including brackets 54. As shown, a pair of the brackets 54 is suitably secured to each end of the rack 52, as by welding. The brackets 54 of each pair are disposed on opposite sides of the rack, and rack spacers 56 are mount ed between the rack and the brackets.

In the illustrated embodiment, the assembly of the rack 52 and brackets 54 is connected to the pistons 50 on the axis of the cylinder tube in such a manner that the rack assembly is supported as a free member by the sliders 53 and so that floating movement of the pistons is permitted. To this end a pair of spaced piston blocks 60 is fixed to the inner face of each piston 50. A pin 61 is tightly mounted in each block 60 and extends inwardly on a line passing through the piston axis. The inboard ends of the pins 61 are engaged in enlarged clearance holes 62 formed in the adjacent brackets 54. The size of the clearance holes 62 in relation to the pins 61 is sufficient to permit limited movement of the pistons relative to the rack assembly.

In assembling the described actuator, the sliders 53 and brackets 54 are connected to a rack of selected length and this assembly is in turn connected to the pistons 50 by the pins 61. The assembly of the pistons and rack is then inserted into the cylinder tube 11 which is closed by the end caps 12. The pinion and sleeve 35, 36 may then be placed in the cylinder tube so that the sleeve keyway 70 (FIG. 1) will be in a predetermined position when the piston and rack assembly is at one end of the cylinder. This correlation of the pinion and rack positions facilitates later connection of the output shaft 37. Finally, the split housing 25 containing the bearings caps 39 and thrust Washers 40 is assembled around the cylinder tube and bolted together. Shims 71 are preferably placed between the housing halves to provide proper clearance for sleeve shoulders 41.

As will be apparent from the foregoing, the construction and assembly of the actuator 10 is relatively simple and inexpensive. A particularly important feature is the use of commercially available stock for the rack 52 and the construction which permits the rack to be replaced easily, as for purposes of repair or when it is desired to change the amount of pinion rotation by substituting a rack of different length. In the preferred construction, the cylinder tube 11 also can be easily replaced, such as may be desired to accommodate different rack lengths and/or different piston sizes. The new and improved actuator construction is further characterized by the axially offset position of the rack 52 and the connection of the rack assembly to the pistons on lines passing through their axes. Because of this arrangement, the driving forces are transmitted by the pistons in a manner which further reduces any tendency of the pistons to cock or tilt in the cylinder tube.

During operation of the actuator 10, fluid under pressure is alternately introduced into the ends of the tube 11 to effect reciprocation of the piston and rack assembly and consequent rotation of the pinion in opposite directions. When fluid under pressure is introduced into an end of the cylinder tube, such as the right hand end as shown in FIG. 1, the piston to which the pressure is applied is forced against the connected bracket 54 to drive the rack. The other piston in the unpressurized end of the cylinder is prevented from running away from the rack assembly, since it is retained by the pins 61 in the piston blocks 69.

Because of the lost motion connections between the pistons and rack assembly which permit floating movement of the pistons, the rack assembly is essentially freely supported by the sliders 53 so that separation forces between the rack and pinion are not transmitted to the pistons. At the same time, the sliders 53 prevent the rack from bending. Thus, the construction provided by this invention assures that the pistons will freely run in the cylinder and that they will not cock and bind because of high output torque. Another advantage afforded by the sliders 53 is that they control backlash between the rack and pinion.

While the features of the rack construction, the use of rack sliders, and the lost motion connections between the rack assembly and pistons have been disclosed in conjunction with a specific actuator arrangement including the tube 11, the housing 25, and the internally mounted pinion 35, it will be understood that the features also can be embodied in other arrangements. By way of example, these features may be employed to advantage in actuators such as disclosed in US. Patents Nos. 2,844,127 and 2,844,128.

Many other modifications and variations of the invention will be apparent to those skilled in the art in view of the foregoing detailed disclosure. Therefore, it is to be understood that, within the scope of the appended claims, the invention can be practiced otherwise than as specifically shown and described.

What is claimed is: 1. A fluid actuator comprising: (a) a housing assembly having inner wall surfaces defining a chamber, the chamber having spaced end 7. The rotary fluid actuator as claimed in claim 6 wherein said bearing means comprises an elongated member secured to the bottom of said rack and disposed in sliding engagement with the inner wall surface of said portions, 5 cylinder.

(b) a piston reciprocally disposed in each end portion 8. A rotary fluid actuator as claimed in claim 6 wherein of said chamber, said bearing means comprises a plastic rack slider secured (c) a member extending between said pistons, said to the bottom of said rack and disposed in sliding enmember being offset from the axis of said chamber, gagement with the inner wall surface of said cylinder. ((1) bearing means disposed between said member and 10 9. A rotary fluid actuator comprising:

the inner wall surfaces for preventing said member (a) a cylinder, from bending when said actuator is operated, and a rotatably mounted P (e) means connecting each end of said member to the a piston member reciprocally disposed in said cylindj e t piston on it dia t der between each of its ends and said pinion, I

(f) said connecting means including means permitting a ck extending between said piston members limited floating movement of said pistons relative to ill meshing Engagement With Said Pinion, Said Tack said member. being offset from the axis of said cylinder,

2. Afluid actuator comprising: (e) elongated rack sliders connected to the bottom (a) a housing assembly having inner wall surfaces deof said rack and disposed in Sliding engagement With fining a chamber, the chamber having spaced end the inner Wall Surface of Said Cylinder,

portions, (f) bracket members connected to the ends of said (b) a piston reciprocally disposed in each end portion Tack, and

of id h b (g) means forming a lost motion connection between a mgmbef extending between id pistons, each bracket member and the adjacent piston mem- (d) a plastic slider secured to said member and disfor Permitting floating movement of Said Piswh posed i lidi engagement i h h inner 11 members relative to the assembly of said rack and faces of said chamber, bracket members,

(e) a bracket secured to each end of said member, and each of Said mfiahs forming a 10st motion Connec- (f) means forming a lost motion connection between tion ihchldihg a P means fixing Said P to one each bracket and the adjacent piston for permitting 3O P Said members, and the other of Said members limited floating movement of said pistons relative to mg 311 ehlafgfid hole in which Said p is receivedthe assembly of said member and brackets. A rotary fluid actuator Compfisihgi 3. The actuator as claimed in claim 2 wherein the mema Cylinder tube p at its ends and having a Shaft ber is a rack and the rack is offset from the axis of said Opening between ends, cylinder and is connected to the piston on its diameter. h p closing the ends of Said tube, Said p 4. A rotary fluid actuator comprising: having fluid P means fo i a cylinder (c) a split housing having a plurality of sections as- (b) a pinion rotatably joturnalled b t h d f sembled around said tube between its ends, means said actuator, and clamping said sections together on said tube in a fixed (c) an assembly of two pistons and a rack between the Position, Said housing including a Shaft Opening i ton aligned with said tube shaft opening, said housing (d) said assembly being reciprocally mounted in said Surrounding Said tube and Said Shaft Opening to cylinder with the rack in meshing engagement with nf said tube n the areas around the Openings; said pinion, (d) a pinion and shaft in said tube, said shaft project- (c) said assembly including means forming lost motion ing through said aligned shaft openings,

connections between the rack and pistons for per- (e) rotatably journalling said pinion and shaft in said mitting floating piston movement while preventing housing, and

axial separation of the rack and pistons, the assem- (f) a piston and rack assembly reciprocally disposed bly also including means slidably supporting the in said tube and meshing with said pinion for rotatrack as a free member in said cylinder. ing said pinion and shaft; and,

5. The actuator as claimed in claim 4 wherein the rack (g) said assembly including means forming fluid tight is offset from the axis of said cylinder, and wherein said connections between said pistons and the tube on lost motion connections are located on diameters of both sides of said pinion whereby to cause reciprocathe pistons. tion of said assembly on introduction of fluid under 6. A rotary fluid actuator comprising: pressure and to the ends of the tube and means slid- (a) a cylinder, ably supporting said rack it reciprocates.

(b) a pinion rotatably mounted between the ends of 11. A rotary fluid actuator comprising:

said actuator, (a) a cylinder tube,

(c) a piston reciprocally disposed in said cylinder be- (b) end caps closing the ends of said tube, said caps tween each of its ends and said pinion, having fluid ports,

((1) a rack extending between said pistons in meshing (c) a housing secured between the ends of said tube,

engagement with said pinion, said rack being offset (d) a shaft journalled in said housing, from the axis of said cylinder, (e) a pinion fixed on said shaft,

(e) bearing means between said rack and the inner (f) a piston reciprocally disposed in each end portion wall surface of said cylinder, said bearing means of said tube,

extending along the length of said rack a distance (g) a rack extending between said pistons in meshing sufficient to prevent bending during operation of said engagement with said pinion,

actuator, and (h) elongated rack sliders connected to the bottom means n ting each end of said rack to the adof said rack and disposed in sliding engagement with iflceht D OIIitS diameter, the inner wall surface of said tube for preventing (g) said connecting means including means forming a said rack from bending when said actuator is oplost motion connection with each piston so that said erated,

pistons are free to float for a limited distance and (i) a pair of brackets fixed to each end of said rack, so that said rack is freely supported by said bearing (j) a pair of pins fixed to each of said pistons on a line means. passing through its axis, and

(k) each of said brackets being formed with an enlarged hole in which one of said pins is disposed, whereby said pistons are free to float a limited distance relative to the assembly of said rack and brackets and whereby said rack is freely supported by said rack sliders.

12. A fluid actuator comprising:

(a) a housing assembly defining a fluid chamber;

(b) a shaft and pinion structure journaled in the housing and disposed in part within the chamber;

(c) a rack in the chamber and in meshing engagement with the pinion;

(d) first and second spaced pistons positioned in the chamber for reciprocal movement;

(e) said rack having first and second ends;

(f) first and second connecting means respectively connecting the first and second pistons to the first and second ends while permitting limited relative floating movement of the pistons and the rack; and,

(g) said housing having ports for selectively introducing fluid into and exhausting fluid from the ends of the chamber.

13. The device of claim 12 wherein a bearing is carried by the rack for slidable engagement with the housing.

14. The device of claim 12 wherein the housing assembly comprises:

(a) a tube;

(b) end caps closing the ends of the tube;

(c) means clamping the caps against the tube; and,

(d) a split housing around the tube.

15. A fluid cylinder comprising:

(a) a tube defining a fluid chamber;

(b) end caps closing the ends of said tube and each including a port for the introduction and exhaustion of fluid to and from the chamber;

(c) means clamping the end caps against the ends of the tubes;

(d) a piston and rack structure reciprocally carried in the tube and including first and second spaced piston portions in slidable fluid tight engagement with the tube, said piston and rack structure also including a rack portion between and connected to the pistons;

(e) a split housing around the tube and clamped to the tube;

(f) said housing and tube including aligned bores transverse to the axis of the chamber and communicating with the chamber;

(g) a shaft and pinion structure projecting through the bores and including a pinion portion meshing with the rack; and,

(h) a journal bearing positioned in the bores and journalling said shaft.

16. A rotary fluid actuator comprising:

(a) means forming a cylinder;

(b) a pinion rotatably journaled between the ends of said actuator;

(c) an assembly of two pistons and a rack offset from the axis of the cylinder and between the pistons; (d) said assembly being reciprocally mounted in said cylinder with the rack in meshing engagement with said pinion;

(e) said assembly including means forming lost motion connections between the rack and pistons and on diameters of the pistons for permitting floating piston movement and means slidably supporting the rack as a free member in said cylinder; and,

(f) said rack supporting means comprising a plurality of rack sliders formed of plastic bearing material and secured to the bottom of the rack.

References Cited by the Examiner UNITED STATES PATENTS 1,666,108 4/1928 Phillips 92l36 2,737,157 3/1956 Hefner et al. 92-136 3,104,589 9/1963 Rudd 92-l36 SAMUEL LEVINE, Primary Examiner.

4 RICHARD B. WILKINSON, Examiner. 

6. A ROTARY FLUID ACTUATOR COMPRISING: (A) A CYLINDER, (B) A PINION ROTATABLY MOUNTED BETWEEN THE ENDS OF SAID ACTUATOR, (C) A PISTON RECIPROCALLY DISPOSED IN SAID CYLINDER BETWEEN EACH OF ITS ENDS AND SAID PINION, (D) A RACK EXTENDING BETWEEN SAID PISTONS IN MESHING ENGAGEMENT WITH SAID PINION, SAID RACK BEING OFFSET FROM THE AXIS OF SAID CYLINDER, (E) BEARING MEANS BETWEEN SAID RACK AND THE INNER WALL SURFACE OF SAID CYLINDER, SAID BEARING MEANS EXTENDING ALONG THE LENGTH OF SAID RACK A DISTANCE SUFFICIENT TO PREVENT BENDING DURING OPERATION OF SAID ACTUATOR, AND (F) MEANS CONNECTING EACH END OF SAID RACK TO THE ADJACENT PISTON ON ITS DIAMETER, (G) SAID CONNECTING MEANS INCLUDING MEANS FORMING A LOST MOTION CONNECTION WITH EACH PISTON SO THAT SAID PISTONS ARE FREE TO FLOAT FOR A LIMITED DISTANCE AND SO THAT SAID RACK IS FREELY SUPPORTED BY SAID BEARING MEANS. 